According to one aspect of the present invention there is provided a method of manufacturing a powder-coated glass product wherein a thermosetting powder is deposited on a glass substrate and the powder is cured to form the coating by heat applied to the powder through the substrate.
In previous methods of powder-coating a glass substrate, heat to cure the deposited powder is applied from above the substrate, rather than as with the present invention, through the substrate. With heat for curing the powder applied through the substrate in accordance with the present invention, the powder cures progressively from the substrate upwardly through the thickness of the powder deposit so as to ensure that gasses are not trapped in the resultant coating and that the resultant coating is generally homogenous without pinhole or ‘fisheye’ defects.
The glass substrate in the method of the invention may be heated prior to deposition of the powder so that the powder adheres to the glass surface as it is deposited. Adhesion may be enhanced by use of an adhesion promoter included within the powder; alternatively, the surface on which deposition is to take place may be pre-treated with the promoter.
Heat may be applied to the powder through the substrate from a source of infra-red radiation which may be mounted within a box having a reflective internal surface. Transmission of the heat to the glass substrate may be mainly by conduction from the box, and to the powder mainly by the radiation through the substrate. The frequency of the infra-red radiation may be regulated from a higher frequency to a lower frequency as the powder progresses from melt towards cure.
Metal foil may be adhered to a back surface of the coating for reduction of thermal stress in the glass substrate, the metal foil extending inwardly from the edges of the coating across the back surface by a distance within the range of 100-150 mm. The thickness of the metal foil may be within the range 75-150 μm.
According to another aspect of the present invention there is provided a powder-coated glass product wherein a glass substrate is backed by a powder coating and metal foil is bonded to the back surface of the coating to extend inwardly from the edges of the product across the back surface by a distance within the range of 100-150 mm for reduction of thermal stress in the glass substrate.
The metal foil may be bonded to the back surface of the coating to extend inwardly from the edges of the product across the back surface by substantially 125 mm, and the thickness of the metal foil may be within the range 75-150 μm.